The discovery of X-rays in 1895 was the beginning of a revolutionary change in our understanding of the physical world.
In the winter of the year of his fiftieth birthday, and the year following his appointment to the leadership of the University of Würzburg, Rector Wilhelm Conrad Roentgen noticed a barium platinocyanide screen fluorescing in his laboratory as he generated cathode rays in a Crookes tube some distance away. Leaving aside for a time his duties to the university and to his students, Rector Roentgen spent the next six weeks in his laboratory working alone and sharing nothing with his colleagues.
Three days before Christmas he brought his wife into his laboratory, and they emerged with a photograph of the bones in her hand and of the ring on her finger. The Würzburg Physico-Medical Society was the first to hear of the new rays that could penetrate the body and photograph its bones. Roentgen delivered the news on Dec. 28, 1895.
Emil Warburg relayed it to the Berlin Physical Society on Jan. 4, 1896. The next day the Wiener Press carried the news, and the day following, word of Roentgen's discovery began to spread by telegraph around the world.
Roentgen was well aware of the enormous help this technology could offer in diagnosing and treating previously undetectable internal ailments. Within a year after he published his findings, X-ray photographs were being used to assist doctors performing surgery and on the battlefield to locate bullets in the bodies of wounded soldiers. The impact of X-rays on the medical field has only increased since then with the development of fluoroscopy, angiography, and tomography.
X-rays are basically the same thing as visible light rays. Both are wavelike forms of electromagnetic energy carried by particles called photons. The difference between X-rays and visible light rays is the energy level of the individual photons. This is also expressed as the wavelength of the rays.
In general, X-rays have a short wavelength and may easily penetrate through a subject. Amounts of penetrating X-rays are affected by the density of an area of the subject. That is, an area of the subject may be indirectly observed due to the amounts of X-rays penetrating the subject. X-ray image sensors detect the amounts of X-rays penetrating the subject. The X-ray sensors detect the amounts of penetrated X-rays and may display a form of an area of the subject on a display device. X-ray sensors may be generally used in examination apparatuses such as a medical examination apparatus.
Today, digital X-ray imaging devices are rapidly replacing photographic film-based X-ray imaging devices in medical applications (e.g., dental applications and mammography). In addition to the inherent advantages associated with digital imaging, digital X-ray imaging devices can have the added benefit of being able to reduce the radiation dose received by a patient.
Typically, the readout circuit of an X-ray sensor converts each photon into an electrical voltage. The dynamic range of the X-ray sensor may be limited. For example, when a strong X-ray is emitted, the readout circuit may not go over a certain readout voltage. In such instances, it may be measured at the same output level as a weaker X-ray. With current readout integrated circuits, the charge sensitive amplifier (CSA) gain is fixed. Therefore, there is no way to increase the intensity of the X-rays. Thus, when the X-rays are converted into an image, the intensity is not increased.
There is a need to increase the dynamic range of an X-ray sensor. Heretofore, several unsuccessful attempts have been made to address these shortcomings.
U.S. Patent Application 20110108735 A1 discloses a high dynamic range X-ray detector with improved signal to noise ratio.
U.S. Pat. No. 5,789,737 discloses a high dynamic range segmented pixel sensor array.
U.S. Pat. No. 6,633,657 discloses a method and apparatus for controlling the dynamic range of a digital diagnostic image.
U.S. Patent Application 20090168966 discloses a medical digital X-ray imaging apparatus and medical digital X-ray sensor.
U.S. Patent Application 20030035510 discloses a sensor arrangement and method in digital X-ray imaging.
U.S. Patent Application 20090108207 discloses a CMOS sensor adapted for dental X-ray imaging.
U.S. Patent Application 20100171038 discloses a sensor unit for an X-ray detector and associated production method.
U.S. Patent Application 20100102241 discloses a system and method for automatic detection of X-rays at an X-ray sensor.
None of these references, however, teach a readout circuit for increasing the dynamic range of an X-ray sensor.